Modularity of an aircraft turbomachine

ABSTRACT

An aircraft turbomachine having a longitudinal axis includes a high-pressure (HP) body, a low-pressure (LP) body, a fan, and a reduction gear having an epicyclic gear train. The turbomachine includes three modules: a first module having the LP turbine and the LP shaft, a second module having the LP compressor and a journal secured to the rotor of the LP compressor, and a third module having an input shaft of the reduction gear, this input shaft having an upstream end for coupling to a sun gear of the reduction gear and a downstream end comprising first splines that are oriented parallel to the axis and are configured to be engaged in second complementary splines of said second module.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to solutions for facilitating themodularity of an aircraft turbomachine.

TECHNICAL BACKGROUND

The prior art includes, in particular, the documents WO-A1-2015/075345,US-A1-3,631,688, FR-A1-2,975,149, U.S. Pat. Nos. 3,958,887 and3,469,868.

An aircraft turbomachine is often constructed as an assembly of modules,each of which may have fixed portions and moving portions. A module isdefined as a sub-set of an engine that has geometric characteristics atthe level of its interfaces with the adjacent modules that aresufficiently precise for it to be delivered individually, and which hasbeen separately balanced when it comprises rotating portions. Theassembly of the modules allows to build a complete engine, reducing to aminimum the balancing and matching operation of the interfacing parts.

The modularity of a turbomachine is a key element for its maintenance.Indeed, during an intervention, the parts must be easily accessiblewithout having to dismantle a large number of portions of the engine. Inpractice, we try to achieve a breakdown into a few major modules. Forexample, for a turbomachine with an upstream fan (the terms “upstream”and “downstream” are to be understood in relation to the flow of gasesin the turbomachine), we are looking for a division into three modules:a first major module for the front portion comprising the fan and the LPcompressor, a second major module for the portion comprising the HP bodyand a third major module for the rear portion of the engine comprisingthe LP turbine and the LP shaft. It is thus understood that the LP bodyis divided into two modules.

The two modules of the LP body are fixed to each other by means of a nutthat extends around the axis of the turbomachine and serves to axiallyclamp the fan shaft to the LP shaft.

During a maintenance operation, this nut must be unscrewed by means of atool that is inserted into the turbomachine along its longitudinal axis,and thus inside the LP shaft and/or the fan shaft.

This maintenance is particularly difficult on a turbomachine with areduction gear in the front or upstream portion. The problem in thiscase is the accessibility of the nut. The reduction gear is locatedupstream of the nut and must be partially removed to gain access to thenut. In addition, the access to the nut must be achieved with complextools that present the risk of mishandling and damaging the engine.

In this case, the modularity of the first major module is lost. Inaddition, the second major module and the third major module must bedisassembled independently.

However, the modularity of the first module is important when thismodule includes a reduction gear. The reduction gear is housed in alubrication enclosure which should preferably be kept closed duringmaintenance to prevent oil leakage. To avoid dismantling this enclosure,there is a tendency to increase the internal diameter of the reductiongear so that it is larger than the diameter of the nut, thus allowingthe nut to be removed from the inside of the reduction gear. However,this solution is detrimental to the size of the reduction gear and theoverall performance of the turbomachine.

In order to improve their propulsive efficiency, the turbomachines tendto increase by-pass ratios, which generally translates into an increasein fan size (diameter and axial dimension). This makes access to the nutof the LP shaft even more complex due to the lengthening of the toolrequired to access it.

In addition, some turbomachines, such as those with an Unducted SingleFan (USF), are particularly long and the modules of the HP and LP bodieshave very small internal diameters, which makes it difficult orimpossible for the tool to access the nut.

The present invention provides a solution to at least some of the aboveproblems that simplifies the modularity of an aircraft turbomachine.

SUMMARY OF THE INVENTION

According to a first aspect, the invention relates to a set of shaftsfor an aircraft turbomachine, this set comprising:

-   -   a first shaft comprising external splines oriented parallel to        an axis of rotation of the shaft,    -   a second shaft comprising internal splines complementary to said        external splines, this second shaft being axially engaged with        the first shaft and these shafts rotating as one by engagement        of their splines, and    -   a system for axially locking the shafts with respect to each        other,

characterised in that said system comprises screws which are orientedradially with respect to said axis, each of these screws being screwedinto a first orifice of one of the shafts and comprising a free endcapable of being engaged in a second orifice of the other of the shafts,each of these screws being movable by screwing from a first radialposition in which its free end is engaged in said second orifice andensures axial locking of the shafts, and a second radial position inwhich its free end is disengaged from said second orifice and ensuresaxial unlocking of the shafts.

The set of shafts according to the invention is particularly suitablefor facilitating the modularity of an aircraft turbomachine and can forexample be used in the interface between two modules of an aircraft andmore particularly in the interface between two shafts of these modules.

The coupling between the two shafts is made by splines. The splines runparallel to each other and are engaged by simple axial translation ofthe first shaft into the second shaft.

There are two types of spline couplings, the first coupling wherein thesplines are free to slide axially within each other. A firstdisadvantage of this coupling is that the splines need to be lubricatedand it is therefore necessary to have an oil sprinkler nearby. In aturbomachine with a reduction gear, the splines could be housed in theenclosure of the reduction gear for lubrication, but the disengagementof the splines during a maintenance operation would result in theenclosure being opened.

The second type of spline coupling is one in which the splines areaxially locked together, and it is this technology that is used in thepresent invention. The advantage is that the splines do not need to belubricated. However, an axial locking system must be provided for theshafts and thus the splines within each other.

According to the invention, this locking is provided by radial screws.In other words, the locking screws of the shafts do not run parallel tothe axis but radially with respect to this axis. The screws can beevenly distributed around the axis and their number is adapted inparticular according to the diameters of the shafts and the maximumtorque to be transmitted between these shafts.

The set according to the invention may comprise one or more of thefollowing characteristics, taken alone from each other, or incombination with each other:

-   -   the first position is a radially external position, and the        second position is a radially internal position;    -   each of the screws comprises a radially internal end carrying a        bearing head, and a radially external free end comprising a        recessed cavity configured to receive a tool for        screwing/unscrewing the screw;    -   a ring is fixed in each of said second orifices and comprises an        internal bore which has a frusto-conical segment configured to        cooperate with said free end of the screw for centring the        latter in said second orifice; the advantage of providing a        centring ring in each second orifice is that this ring can be        replaced in the event of wear by limiting the impact on the        shaft;    -   each ring is crimped into the corresponding second orifice;    -   a socket is mounted in each of said first orifices and comprises        an internal thread for screwing the corresponding screw; the        advantage of providing a threaded socket in each first orifice        is that this socket can be replaced in the event of wear,        limiting the impact on the shaft    -   each socket comprises an external annular collar for bearing on        the corresponding shaft;    -   a retaining shell is mounted inside the first shaft and        comprises a first cylindrical rim which extends at least partly        opposite said first and second orifices and which is configured        to radially retain the screws when in their respective second        positions;    -   the collar of each socket is radially interposed between the        shaft and a second cylindrical rim of the shell; and    -   the shell comprises an external cylindrical centering surface        configured to cooperate with an internal cylindrical surface of        the first shaft, this internal cylindrical surface comprising an        annular groove for mounting an annular ring of axially retaining        the shell relative to the first shaft.

The present invention also relates to an aircraft turbomachine,comprising at least one set as described above.

Advantageously, said set is surrounded by at least one stator casingwhich comprises at least one radial orifice configured to allow thepassage of a tool for screwing/unscrewing said screws.

According to another aspect, the invention relates to an aircraftturbomachine, this turbomachine having a longitudinal axis andcomprising:

-   -   a high-pressure body called HP comprising an HP shaft for        connecting a HP compressor rotor to a HP turbine rotor, this HP        shaft extending along said axis,    -   a low-pressure body called LP comprising a LP shaft for        connecting a LP compressor rotor to a LP turbine rotor, this LP        shaft extending along said axis and inside the HP shaft,    -   a fan connected to a fan shaft, and    -   an epicyclic reduction gear connecting the LP shaft to the fan        shaft

characterised in that the LP body comprises three modules:

-   -   a first module comprising the LP turbine and the LP shaft, the        LP shaft comprising a downstream end coupled to the rotor of the        LP turbine,    -   a second module comprising the LP compressor and a journal        secured to the rotor of the LP compressor, this journal being        configured to be coupled in rotation to an upstream end of the        LP shaft and to be immobilised axially on this end by screwing a        nut onto a thread on the shaft, and    -   a third module comprising an input shaft of the reduction gear,        said input shaft comprising an upstream end for coupling to a        sun gear of the reduction gear and a downstream end comprising        first splines which are oriented parallel to said axis and which        are configured to be engaged in complementary second splines of        said second module, radially oriented screws being carried by        one of the second and third modules and intended to be engaged        in the other of the second and third modules in order to axially        lock the first and second splines in each other.

The LP body of the turbomachine is thus divided into three modulesinstead of two as in most previous turbomachines. The first module is aconventional one, comprising the LP turbine and the LP shaft. This LPshaft extends along the axis of the turbomachine and its downstream endis coupled to the rotor of the LP turbine.

The second module comprises the LP compressor, the rotor of which isconventionally connected to a journal. As in the prior art, this journalis engaged on the LP shaft and secured to the latter by a nut screwed onaxially from upstream. This second module is coupled by splines to athird module comprising the input shaft of the reduction gear.

These splines are axially locked by radial screws. When the screws arein the unscrewed position, it is understood that the third module can bedismantled and removed from the second module.

The third module with the reduction gear can be disassembled and removedfrom the turbomachine before accessing the unscrewing nut of the secondmodule from the first module. The advantage of this is that thereduction gear can have an internal diameter smaller than the diameterof the nut, which is no longer removed from the inside of the reductiongear. The locking screws of the second and third modules are radiallyoriented and can therefore be unscrewed by a tool oriented in the samedirection, which is also not obstructed by the reduction gear.

The turbomachine according to the invention may comprise one or more ofthe following characteristics, taken in isolation from each other, or incombination with each other:

-   -   the fan is of the unducted type;    -   the reduction gear is located in a lubrication enclosure, said        first and second splines being located outside this enclosure;    -   the first and second splines are interposed axially between two        annular seals of the enclosure, which are mounted between the        input shaft and an annular cover of the enclosure mounted around        the input shaft;    -   a first of the seals, located upstream of the first and second        splines, is a segmented radial seal, and a second of the        segmented seals, located downstream of the first and second        splines, is a labyrinth seal;    -   one of the seals is interposed axially between said first and        second splines on the one hand and said screws on the other        hand;    -   the second module comprises an upstream shaft segment comprising        said second splines and mounting orifices for said screws, and a        downstream shaft segment coupled or connected to said journal,        said shaft segments comprising annular flanges secured together        by screws oriented parallel to said axis;    -   the upstream shaft segment comprises a first radial annular wall        the external periphery of which is connected to a first of the        flanges, the downstream shaft segment comprises a second radial        annular wall the external periphery of which is connected to a        second of the flanges, said first and second annular walls        extending opposite each other and imparting a bending        deformation capability to the second module in operation; this        type of connection provides flexibility to the module and is        commonly referred to as a “flex coupling”; and    -   the turbomachine comprises a stator casing which surrounds the        LP and HP bodies and which comprises at least one radial orifice        configured to allow the passage of a tool for        screwing/unscrewing said radial screws.

The invention also relates to a method of dismantling a turbomachine asdescribed above, characterised in that it comprises the steps of:

-   -   unscrewing the radial screws so as to axially unlock said first        and second splines,    -   retracting the third module from the second module,    -   unscrewing the nut from inside the fan and the reduction gear,        and    -   retracting the second module from the first module.

Advantageously, the radial screws are unscrewed by means of at least oneunscrewing tool which is inserted through said or each orifice of thecasing.

BRIEF DESCRIPTION OF THE FIGURES

Further characteristics and advantages of the invention will becomeapparent from the following detailed description, for the understandingof which reference is made to the attached drawings in which:

FIG. 1 is a schematic half-view in axial section of an aircraftturbomachine;

FIG. 2 is a schematic perspective view and axial section of a set ofshafts in the sense of an aspect of the invention;

FIG. 3 is a schematic cross-section of the set shown in FIG. 2 ;

FIG. 4 is a schematic perspective view of a system for axially lockingsplines of the set of FIG. 2 , and shows screws in an unlocked position,

FIG. 5 is a schematic cross-section of the axial locking system with thescrews in the unlocked position,

FIG. 6 is a schematic cross-section of the axial locking system with thescrews in a locking position,

FIG. 7 is a larger scale view of a portion of FIG. 6 ;

FIG. 8 is a similar view to FIG. 1 and illustrates a first step of amethod according to the invention for dismantling an aircraftturbomachine;

FIG. 9 is a larger scale view of a portion of FIG. 8 ; and

FIGS. 10 a-10 c are similar views to FIG. 1 and illustrate further stepsin the disassembly method.

DETAILED DESCRIPTION OF THE INVENTION

Reference is first made to FIG. 1 which illustrates an aircraftturbomachine, which in this case is an unducted single fan (USF)turbomachine 10, although the aspects of the invention are not limitedto this particular type of turbomachine.

The turbomachine 10 is modular and comprises several modules assembledtogether. The reference A refers to the longitudinal axis of theturbomachine 10 which is generally the axis of rotation of its rotors.

A first module 12 is a high pressure or HP module and comprises an HPcompressor 14 and an HP turbine 18. The rotor of the HP compressor 14 isconnected by a HP shaft 16 to the rotor of the HP turbine 18. This HPmodule 12 further comprises the annular combustion chamber 20 which isaxially interposed between the HP compressor 14 and the HP turbine 18.

The low pressure or LP body of the turbomachine 10 is itself dividedinto three modules:

-   -   a first module 22 comprising the LP turbine 24 and the LP shaft        26, the LP shaft comprising a downstream end coupled to the        rotor of the LP turbine,    -   a second module 28 comprising the LP compressor 30,    -   and a third module 32 comprising the input shaft 34 of a        reduction gear 36 of the turbomachine.

The turbomachine 10 is in fact equipped with an epicyclic reduction gear36 which classically comprises a sun gear 38 centred on the axis A, aring gear 40 which extends around the sun gear 38, and planet gearswhich are arranged between the sun gear and the ring gear, and which arein mesh with them and carried by a planet carrier 42. In this case, thering gear 40 is immobile and fixed to a stator of the turbomachine,which in this case is an inlet casing 44. The sun gear 38 is mobile inrotation and coupled to the input shaft 34, and the planet carrier 42 isalso mobile in rotation and coupled to a shaft 46 of the fan 48. The fan48 is therefore driven in rotation by the input shaft 34 through thereduction gear 36.

The reduction gear 36 is located in a lubrication enclosure 50 whichextends around the axis A and is therefore generally annular in shape.At its internal periphery, the enclosure 50 is delimited by the fanshaft 46 and the inlet shaft 34. At its external periphery, theenclosure 50 is delimited by the inlet casing 44 which extends aroundthe reduction gear 36. At its upstream end, the enclosure 50 isdelimited by an annular support 52 of bearings 54, 56. This support 52has an external periphery which is attached to the inlet casing 44 andan internal periphery which holds bearing rings of the roller bearings54, 56, internal rings of which are attached to the fan shaft 46.Finally, the enclosure 50 is closed at its downstream end by an annularcover 58 which is carried by the inlet casing 44 and the internalperiphery of which surrounds the inlet shaft 34 in a sealed manner.

An intermediate casing 60 is interposed between the LP compressors 30and HP 14, an inter-turbine casing 62 is interposed between the HPturbines 18 and LP 24, and an exhaust casing 64 is located downstream ofthe LP turbine 24.

The LP compressor 28 and the HP module 12 are surrounded by an annularcasing 66, an upstream end of which comprises an annular flange 66 a forfastening an annular flange 44 a of the inlet casing 44, and adownstream end of which comprises an annular flange 66 b for fasteningan annular flange 64 a of the exhaust casing 64.

In addition to the LP compressor 30, the second module 28 comprises ajournal 68 which is rotationally secured to the rotor of the LPcompressor, and which is configured to be rotationally coupled to anupstream end of the LP shaft 26 and to be axially immobilised on thisend by screwing a nut 70 onto a thread of the LP shaft 26.

In the example shown, the journal 68 is engaged axially from theupstream on the upstream end of the LP shaft 26. The nut 70 is engagedaxially from upstream on the upstream end of the shaft 26 and is screwedon until it axially clamps the journal 68 against an annular shoulder orthe like of the shaft 26.

Although schematic, it can be seen from FIG. 1 that the nut 70 has adiameter which is greater than the internal diameter of the input shaft34. This means that this input shaft 34 must be dismantled and removedin order to remove the nut 70.

The second module 28 further comprises a shaft 72 divided into twosegments 72 a, 72 b respectively upstream and downstream. The shaftsegments 72 a, 72 b are fixed to each other by clamping.

The upstream segment 72 a is coupled to the input shaft 34 and comprisesat its downstream end a radially external fastening flange 72 aa. Thisflange 72 aa is located at the external periphery of a radial annularwall 72 ab of the downstream end of the segment 72 a.

The downstream segment 72 b is secured in rotation to the journal 68 andthe rotor of the LP compressor 30 and comprises at its upstream end aradially external fastening flange 72 ba. This flange 72 ba is locatedat the external periphery of a radial annular wall 72 bb of the upstreamend of the segment 72 b.

The flanges 72 aa, 72 ba are applied axially against each other andinclude axial screw mounting orifices (not visible) for fastening theflanges together. This configuration of the flanges 72 aa, 72 ba and theradial walls 72 ab, 72 bb allows for a flexible connection. This meansthat the shaft can withstand misalignment between the upstream anddownstream portions, which is particularly interesting in the case of arelatively long engine

The invention provides a solution to facilitate the modularity of theturbomachine 10 by means of a particular device for coupling the modules28, 32 and in particular the shaft 72 of the second module 28 with theinput shaft 34 of the third module 32.

FIGS. 2 to 7 illustrate an embodiment of this device in which theelements already described in the foregoing are designated by the samereferences.

The input shaft 34 of the module 32 is coupled to the shaft 72 of themodule 28 and more specifically to the shaft segment 72 a by a splinecoupling 74, 76. The input shaft 34 includes adjacent its downstream endinternal splines 74 which are oriented parallel to the axis A and areconfigured to engage on complementary external splines 76 of the shaftsegment 72 a.

The spline coupling 74, 76 is here of the axial locking type and thislocking is ensured by screws 78 oriented in radial direction withrespect to the axis A.

The screws 78 are preferably evenly distributed around the axis A. Theirnumber is for example between 6 and 12.

Each of the screws 78 is carried by and screwed into one of the shafts34, 72 and intended to be engaged with the other of the shafts toaxially lock the splines 74, 76 into each other. It is understood thateach screw 78 is mobile in the radial direction by screwing from a firstradial position of axial locking of the shafts to a second radialposition of axial unlocking of the shafts, and vice versa.

In the illustrated example, as best seen in FIGS. 4 to 7 , each screw 78is screwed into an orifice 80 in the shaft segment 72 a and comprises afree end adapted to be engaged in an orifice 82 of the shaft 34. Eachscrew 78 is mobile by screwing from the first radial position, which isa radially external screwing and tightening position of the screw, tosaid second radial position, which is a radially internal unscrewing andloosening position.

Each screw 78 comprises a threaded body which is elongate along a radialaxis with respect to axis A and has one longitudinal (radially external)end free and the opposite longitudinal (radially internal) end connectedto a head 84. The body of each screw 78 is intended to be screwed intoone of the orifices 80, the head 84 of each screw is intended to rest onthe shaft segment 72 a in the first tightening position, and the freeend of each screw is intended to be engaged in one of the orifices 82 ofthe shaft 34 in this first position in order to axially lock the splines74, 76 and the shafts 34, 72.

Each screw 78 is rotated and screwed in by means of a tool which mustalso have a radial or quasi-radial orientation with respect to the axisA. According to one aspect of the invention, the screwing and unscrewingof each screw is carried out radially from the outside and not from theinside of the turbomachine. The tool must therefore have access to andbe able to engage the radially external end of each screw 78. Thus, thetool is not intended to be engaged with the head 84 of each screw 78 butinstead with the free end of the screw, which comprises for example arecess cavity 81, as schematically shown in FIGS. 4 and 7 .

This recess 81 may have a polygonal or, for example, hexagonalcross-sectional shape so as to receive a hexagonal fitting of the tool,for example. Alternatively, it could be of the Torx® type.

A tool 83 is shown schematically in FIGS. 1, 2 and 9 for unscrewing thescrews 78, as well as screwing them in. This tool 83 has an elongatedshape and is engaged through one or more of the orifices 85 of theturbomachine 10. These orifices 85 may be located on stator elements ofthe turbomachine, such as the intermediate casing 44 or the casing 66for example. These orifices 85 are, for example, endoscopy orifices,i.e., orifices that are generally used for endoscopic inspection of theturbomachine. Naturally, these orifices must be aligned with each otherand as far as possible with the axles of the screws 78. The rotation ofthe shaft 34 allows access to the screws 78 one after the other throughthe orifices 85.

In the example shown, a ring 86 is fixed in each orifice 82 of the shaft34. This ring 86 comprises an internal bore which has a frusto-conicalsegment 86 a configured to cooperate with the free end of the screw 78for centring the latter in the orifice 82. The segment 86 a is flaredradially towards the inside. The ring 86 is here crimped into theorifice 82 and comprises at its radially external end a peripheral rim86 b intended to be plastically deformed and pressed against an internalrim 82 a of the orifice 82 (see FIG. 5 for example). It is thereforeunderstood that the ring 86 is inserted radially from the inside intothe orifice 82 and then crimped into the orifice by deformation of itsrim 86 b.

Furthermore, in the example shown, each screw 78 is not directly screwedinto one of the orifices 80 but into a socket 88 mounted in thatorifice. This socket 88 has an internal thread 88 a for screwing in thescrew 78 and also comprises at its radially internal end an annularcollar 88 b for bearing on a boss of the shaft 72 (see FIG. 5 forexample).

The socket 88 may be shrink-fitted into the orifice 80 and comprise anexternal cylindrical surface clamped into an internal cylindricalsurface of the orifice 80. The socket 88 is engaged radially from theinside into the orifice 80 until the collar 88 b rests on the boss ofthe shaft 72. The socket 88 and the ring 86 can be changed if theirthread wears out so that the whole shaft does not have to be changed.

Advantageously, a retaining shell 90 is mounted inside the shaft 72 andhas the function of retaining the screws 78 and thus rendering themcaptive when in their unscrewed positions.

The shell 90 is annular in shape and extends around the axis A. Itcomprises a first cylindrical rim 92 which faces downstream and extendsat least partly opposite the orifices 82 and is configured to radiallyretain the screws 78 when in their unscrewed positions, as illustratedin FIGS. 4 and 5 .

The shell 90 preferably comprises an external cylindrical centeringsurface 90 a configured to cooperate with an internal cylindricalsurface of the shaft 72 to provide centering of the shell upon mounting.The internal cylindrical surface of the shaft 72 may comprise an annulargroove 94 for mounting an annular ring (not shown) for axially retainingthe shell 90 against, for example, the aforementioned boss of the shaft72.

The shell 90 further comprises a second cylindrical rim 94 which facesdownstream and extends partly around this boss. The collars 88 b of thesockets 88 are radially interposed between the boss and this rim 96,which provides radial retention of the sockets in the orifices 80 andalso renders them captive or radially immobile.

FIGS. 4 and 5 show the screws 78 in their unscrewed positions to unlockthe shafts 34, 72. It can be seen that the heads 84 of the screws 78rest radially on the rim 92 of the shell 90 and that their free ends areat a radial distance from the orifices 82. The screws 78 therefore donot interfere with the movement of the shafts 34, 72 with respect toeach other and the axial disengagement of the splines 74 from eachother.

FIGS. 6 and 7 show the screws 78 in their screwed-in positions foraxially locking the shafts 34, 72. It can be seen that the heads 84 ofthe screws 78 are at a radial distance from the rim 92 of the shell 90and that their free ends are engaged in the rings 86 of the orifices 82.The screws 78 prevent the shafts 34, 72 from moving relative to eachother and axially disengaging the splines 74 from each other.

With regard to the splines 74, 76, FIGS. 2 and 3 in particular show thatthey are located outside the lubrication enclosure 50 of the reductiongear 36, and more precisely downstream from it.

In the example shown, the splines 74, 76 are located axially between twoannular seals 98, 100 of the enclosure 50, namely the two seals locatedat the downstream end of the enclosure 50 and mounted between the cover58 and the input shaft 34.

The seal 98 upstream of the splines 74, 76 is a segmented radial seal,and the seal 100 downstream of the splines is a labyrinth seal. Thescrews 78 are located downstream of the splines 74, 76 and the seals 98,100, with the seal 100 axially interposed between the splines and thescrews 78.

It can also be seen from FIGS. 2 and 3 that the diameters of the seals98, 100, the splines 74, 76 and the screws 78 are relatively close toeach other.

Reference is now made to FIGS. 8 to 10 c, which illustrate steps fordismantling the turbomachine 10 of FIG. 1 . It will be understood thatthe assembly or reassembly of the turbomachine can be used by repeatingthese operations in reverse order.

FIG. 8 is similar to FIG. 1 and FIG. 9 is a larger scale view in whichsome references to the set of shafts according to the inventiondescribed above are indicated.

A first step of the method consists of inserting the tool 83 through theorifices 85 of the turbomachine 10 and then unscrewing the screws 78,one after the other, so as to bring them from their screwed positions totheir unscrewed positions. This can be achieved with a single toolengaged in a single orifice 85 or in a single series of aligned orifices85 if the shafts 34, 72 are rotated after each unscrewing so that thenext screw to be unscrewed is aligned with the orifice(s) 85.Alternatively, in the event that there are as many orifices 85 or seriesof orifices 85 as there are screws 78, a same tool 83 could be insertedin turn into each of these orifices or series of orifices.

The screws 78 are then in the unscrewed position so the splines 74, 76and shafts 34, 72 are free to move axially with respect to each other orto each other. This means that the third module 32 can be separated fromthe second module 28. To do this, it may be necessary to disengage theflanges 44 a, 66 a from each other. After this separation, the entireupstream portion of the turbomachine, which includes the module 28 butalso the reduction gear 36, the fan 48 and the intermediate casing 44,can be removed from the rest of the turbomachine shown in FIG. 10 a . Itis thus understood that the enclosure 50 remains closed, which limitsthe risk of oil leakage.

Another step in the method consists of unscrewing the nut 70 that holdsthe two modules 28, 22 together. It is unscrewed and removed fromupstream. This gives the situation as shown in FIG. 10 b.

A next step in the method is to disengage the flanges 66 b, 64 a fromeach other and remove the exhaust casing 64 axially from downstream(FIG. 10 c ). The first module 22 can then be removed by moving itaxially downstream from the second module 28 and the HP module 12 andthe inter-compressor 60 and inter-turbine 62 casings.

The various modules of the turbomachine 10 are disconnected from eachother and can undergo maintenance by reassembling the turbomachine.

1. An aircraft turbomachine having a longitudinal axis, the turbomachinecomprising: a high-pressure (HP) body comprising an HP shaft forconnecting an HP compressor rotor to an HP turbine rotor, the HP shaftextending along the longitudinal axis; a low-pressure (LP) bodycomprising an LP shaft for connecting an LP compressor rotor to an LPturbine rotor, the LP shaft extending along the longitudinal axis andinside the HP shaft; a fan connected to a fan shaft; and an epicyclicreduction gear connecting the LP shaft to the fan shaft, wherein the LPbody comprises: a first module comprising the LP turbine and the LPshaft, the LP shaft comprising a downstream end coupled to the rotor ofthe LP turbine; a second module comprising the LP compressor and ajournal secured to the rotor of the LP compressor, the journal beingconfigured to be coupled in rotation to an upstream end of the LP shaftand to be immobilized axially on this end by screwing a nut onto athread on the shaft; and a third module comprising an input shaft of thereduction gear, the input shaft comprising an upstream end for couplingto a sun gear of the reduction gear and a downstream end comprisingfirst splines which are oriented parallel to the longitudinal axis andwhich are configured to be engaged in complementary second splines ofsaid second module, and radially oriented screws being carried by one ofthe second and third modules and intended to be engaged in the other ofthe second and third modules in order to axially lock the first andsecond splines in each other.
 2. The turbomachine of claim 1, whereinthe fan is of the unducted type.
 3. The turbomachine of claim 1, whereinthe reduction gear is located in a lubrication enclosure, and whereinthe first and second splines are located outside of the lubricationenclosure.
 4. The turbomachine of claim 3, wherein the first and secondsplines are interposed axially between two annular seals of thelubrication enclosure, which are mounted between the input shaft and anannular cover of the enclosure mounted around the input shaft.
 5. Theturbomachine of claim 4, wherein a first of the seals located upstreamof the first and second splines is a segmented radial seal, and a secondof the segmented seals located downstream of the first and secondsplines is a labyrinth seal.
 6. The turbomachine of claim 4, wherein oneof the seals is interposed axially between the first and second splines,on the one hand, and the radially oriented screws, on the other hand. 7.The turbomachine of claim 1, wherein the second module comprises anupstream shaft segment comprising the second splines and orifices formounting the radially oriented screws, and a downstream shaft segmentcoupled to the journal, the shaft segments comprising annular flangessecured together by screws oriented parallel to the longitudinal axis.8. The turbomachine of claim 7, wherein the upstream shaft segmentcomprises a first radial annular wall, the external periphery of whichis connected to a first of the flanges, wherein the downstream shaftsegment comprises a second radial annular wall, the external peripheryof which is connected to a second of the flanges, and wherein the firstand second annular walls extend opposite each other and imparting abending deformation capability to the second module in operation.
 9. Theturbomachine of claim 1, further comprising a stator casing whichsurrounds the LP and HP bodies and which comprises at least one radialorifice configured to allow the passage of a tool forscrewing/unscrewing the radially oriented screws.
 10. A method ofdismantling a turbomachine according to claim 1, the method comprising:unscrewing the radially oriented screws to axially unlock first andsecond splines; retracting the third module from the second module;unscrewing the nut from inside the fan and the reduction gear; andretracting the second module from the first module.
 11. The method ofclaim 10, wherein the turbomachine further comprises a stator casingsurrounding the LP and HP bodies and having at least one radial orificeconfigured to allow the passage of a tool, wherein the method furthercomprises unscrewing the radially oriented screws by inserting the toolthrough the at least one radial orifice in the casing.